This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C xc2xa7119 from an application entitled Recovery Apparatus And Method Of Instability Head In A Disk Drive earlier filed in the Korean Industrial Property Office on Feb. 19, 2001, and there duly assigned Ser. No. 2001-8137 by that Office.
1. Field of the Invention
The present invention relates to an apparatus and method for controlling a disc drive and, more particularly, to an apparatus and method for restoring stability to a head of a hard disc drive, so that instability in a magneto resistive (MR) sensor of the disc drive can be restored through an electric shock.
2. Description of the Related Art
Existing inductive heads have adopted a method of converting variations in magnetic flux of a disc into variations in a voltage of a head coil by winding a coil around ahead core. In this case, an inductance value of the head coil must be lowered for stability of the data signal in an inductive head if the frequency of a data signal is increased, which results in a drop in an inductive voltage of the head and causes unstable detection of the data signal.
A magneto-resistive head (hereinafter, xe2x80x9cMR headxe2x80x9d) has been designed to solve the above problem of existing inductive heads. The MR head is adapted to a data signal having a high frequency by adopting an MR sensor that can easily perceive any variation in the magnetic flux of a disc. In the past, variations in the magnetic flux of a disc were converted into variations in an inductive voltage by means of a head coil in an inductive head, whereas in the MR head, variations in the magnetic flux of a disc are detected with variations in a resistance value through the MR sensor when reading data and recording density per unit area and a S/N ratio per unit area can be enhanced using the existing inductive head structure when writing data.
However, the MR sensor of the MR head has a problem of instability, which is not found in existing inductive heads. The instability of the MR head occurs in an unstable domain of the MR sensor and is mainly due to damage caused by soft electrostatic discharge (ESD), an improper hard bias (or permanent magnet) operation applied to the ends of the MR sensor and so on. If the capacity of the MR head is increased for the purpose of increasing sensitivity per unit area of the MR sensor, the width of the MR head becomes narrow as the number of tracks per inch (TPI) is increased, thus deteriorating the stability of the head. Such instability of the MR head brings about problems in a signal generated by a hard disc drive such as base line popping, base line noise, amplitude spikes and high amplitude asymmetry. Moreover, the instability of the MR head can occur at any point of time, even under normal conditions, such that a manufacturing process inferiority rate is raised and the performance of the hard disc drive is affected greatly.
To solve these problems, many proposals have been suggested, e.g., U.S. Pat. No. 5,650,887 to Moris Musa Dovek et al. and entitled System For Resetting Sensor Magnetization In A Spin Valve Magnetoresistive Sensor and Korean Laid-Open Patent No. 1999-072284. U.S. Pat. No. 5,650,887 discloses a technique in which a servo automatic gain control (AGC) is measured and a reset current is applied to a head only in the event that the measured servo AGC is 20%. Korean Laid-Open Patent No. 1999-072284 discloses a technique in which performance of a head is determined by checking if a servo signal is detected and a reset current is applied in the opposite direction of the head.
However, head instability is determined only by a servo AGC value in the U.S. Pat. No. 5,650,887 patent. That is, the instability test of the head is performed with regard to a current level, into which data is modulated, rather than real data. Therefore, it is difficult to correctly determine if a head is in stable state or not. Similarly, the technique disclosed in Korean Laid-Open Patent No. 1999-072284 has a problem in which the instability head test is not performed directly on data and thus stability of a head cannot be determined.
To solve the above problem, it is an objective of the present invention to provide an apparatus and method for restoring stability to a head of a disc drive, in which instability of a magneto-resistive (MR) head can be easily determined by checking an error detecting rate when reading data during a process of manufacturing a hard disc assembly and improving the instability of the MR head by repetitively applying electric shocks thereto, while checking whether head instability is improved through head performance testing.
Accordingly, to achieve the above objective, there is provided an apparatus for restoring stability to an MR head of a disc drive including: an MR head having a resistance which changes in accordance with magnetic flux recorded on a disc; a signal processing unit for reproducing, in a reading mode, a signal detected by the MR head into data, as it was before being recorded, and for generating a recording current that corresponds to data to be recorded in a recording mode; a controller for performing a predetermined performance test related to data errors that can be used to check the performance of the MR head, using data reproduced in the signal processing unit during a hard disc assembly inspection process, and for generating an electric shock control signal in the event that the output of the performance test is outside of predetermined parameters; and a head feed current controller for applying a reset electric pulse, which has a level higher than the level of the MR head read current, to the MR head when the electric shock control signal is applied.
To achieve the above objective, there is also provided a method of restoring stability to an MR head of a disc drive, during a hard disc assembly inspection process, including the steps of: (a) determining whether the performance value of the MR head is within a predetermined first standard range by performing a predetermined performance test based on read data errors so as to check the performance of the MR head; (b) applying a reset current pulse to the MR head in the event that the result obtained in the step (a) is outside of the predetermined first standard range; (c) performing the predetermined performance test after the step (b) to check the performance of the MR head; (d) is checking whether the result obtained in the step (c) is outside of a predetermined second standard range; and (e) applying the reset current pulse to the MR head; and (i) repeatedly performing steps (c)-(e) when the result is outside of the predetermined second standard range or ending the process of restoring stability to the MR head when the result is within the predetermined second standard range.